Pesticidal or herbicidal compositions

ABSTRACT

A pesticidal or herbicidal composition in particulate form which comprises composite particles. Each of said particles contains a core of an inert substance having a pesticidal herbicide associated therewith and a coating of an electrically resistive material around the core. The particles may also include a second pesticidal material adhering to the electrically resistive coating. The particles carry an electrostatic charge.

This application is a 371 of PCT/GB97/00683, filed Mar. 12, 1997, whichclaims priority of GB9605203.0, filed Mar. 12, 1996.

BACKGROUND OF THE INVENTION

The present invention relates to pesticidal or herbicidal compositions.

The most common domestic insect pests are houseflies, mosquitoes andcockroaches.

The common housefly, Musca domestica, occurs throughout the world indomestic situations. Along with similar species, such as, the lesserhousefly, blowflies and flesh flies, it contaminates food and spreadsdiseases, such as, typhoid and cholera, and also carries the eggs ofparasitic worms.

The housefly is also a problem on refuse tips and is becoming aprogressively greater nuisance in agriculture, where it breeds in deeplitter breeding units for poultry and other animals.

The cockroach is ubiquitous in urban situations in the tropics andsub-tropics and is common in heated buildings in Britain, the rest ofEurope and North America where food is prepared. Large cockroachpopulations are found in sewers and drains and many disease organismshave been isolated from them.

The mosquito is both a severe nuisance pest and vastly important as avector for blood-borne diseases, such as, malaria, yellow fever, dengueand the like.

Control of those insect pests is becoming more urgent as humanpopulations increase and provide more resources for them to breed.

International Patent Application No. WO94/00980 described the ability ofelectrostatically charged powders to adhere to an insect cuticle, to asurface of a plant or to a surface of an insect trap. However,insecticidal powders, for example magnesium silicate or silica particlesimpregnated with an insecticide, do not have the necessarycharacteristics either to be electrostatically charged or to retain suchan electrostatic charge and therefore the particles do not becomeattached firmly to an insect cuticle, to the surface of a plant, or to asurface of an insect trap.

Herbicidal compositions which are in a particulate form also suffer thedisadvantage that the herbicidal particles do not adhere firmly to theplants onto which they are sprayed or dusted.

We have now developed pesticidal or herbicidal compositions which are inparticulate form and which have improved adherent properties so thatthey adhere more firmly to the insect, plant or surface onto which theyare sprayed or dusted.

SUMMARY OF THE INVENTION

Accordingly, the present invention provides a pesticidal or herbicidalcomposition in particulate form which comprises composite particles eachcomprising a core of an inert substrate having a pesticide or herbicideassociated therewith, and a coating of an electrically resistivematerial around the said core, the particles carrying an electrostaticcharge.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a composite particle according to this invention.

FIG. 2 is a graph showing the mean mortality of cockroaches resultingfrom the tests of Example 1.

FIG. 3 is a graph showing the mean mortality of cockroaches resultingfrom the tests of Example 2.

DETAILED DISCLOSURE

By the term “pesticide” as used herein is meant any substance which canbe used in the control of agricultural, natural environmental anddomestic pests, such as insects. Included within this term, therefore,are naturally occurring or synthetic chemical insecticides, fungicides,acaricides, insect growth regulators and chemosterilants;entomopathogens such as bacteria, viruses and fungi; parasites; andbehaviour modifying chemicals such as pheromones, allomones andkairmones. By the term “herbicide” as used herein is meant any substancewhich can be used in agriculture to control or modify plant growth.

The compositions of the present invention comprise a core of an inertsubstrate, i.e. a material which acts merely as a carrier for thepesticide or herbicide and which is chemically and biologically inert.The inert substrate is preferably porous and highly absorbent. Suitableexamples of such materials are silicon dioxide, magnesium silicate(talc), diatomaceous earth, cellulose or natural or synthetic polymerssuch as chitin, chitosan or rubber. The inert substrate may have thepesticide or herbicide associated with it by impregnation into it, ormay have the pesticide or herbicide associated with it in some other wayfor example by adsorption or absorption thereon.

The cores of the composite particles are coated with a coating of anelectrically resistive material, i.e. a material which readily acceptsan electrical charge, such as a wax, a lipid, a natural or syntheticresin or a natural or synthetic polymeric material. Examples of waxeswhich may be used are Carnauba Wax, paraffin waxes, candelilla wax andbees' wax. Examples of polymeric coating materials arepolytetrafluoroethylene, or ethylenic polymers. Examples of resins areshellac and synthetic acrylic resins. An example of a lipid which may beused is lecithin.

The composite particles of the present invention will generally have aparticle size in the range of form 1 to 100 μm, preferably 20 to 60 μm.If the particles are too small then they become hazardous to humanhealth, whilst if they are too large they will then tend to fall off theinsect, plant or other surface to which they are applied either becauseof gravitional forces and/or because there will be insufficientelectrostatic attraction. The thickness of the coating of theelectrically resistive material is not critical, provided that itsurrounds the core of the particles and can readily accept an electriccharge. Generally, the coating material will comprise at least 0.1% byvolume, preferably 5 to 25% by volume of the particles and the core willcomprise up to 99.9% by volume, preferably 75 to 95% by volume of theparticles.

The coating of electrically resistive material may be applied to thecores of the particles by any suitable coating technique such as byfluidised bed coating, spraying or mixing.

The amount of pesticide or herbicide which is impregnated into orassociated with the inert substrate will generally comprise at least0.1% by weight of the inert substrate. The amount of the pesticide orherbicide will depend upon the intended release rate from thecomposition and the length of intended duration of release. It will alsodepend upon the nature of the electrically resistive coating and otherfactors.

It is known that insects carry an electrostatic charge. In the case ofthe cockroach, the outside of its cuticle is positively charged, with anelectrostatic gradient across the cuticle (Beament, J. W. L. in NatureLond. Vol. 191, 1961, pp 217-221).

Accordingly, it is preferred if the particles of the compositions of theinvention are electrostatically charged to have an opposite polarity tothat of the pest against which they are targeted. In this manner, theadhesion of the charged particles to the pest is improved.

The pesticide which is used in the present invention may be specificallytargeted to the control of particular pests. For example, an insecticidemay be applied to sexually mature male insects so that it spreads amongthe rest of the population during mating or by contact during swarming.The insecticide is unlikely to spread to other species of insect whentransmitted in this way.

Each pesticide may be chosen to have a narrow spectrum of action.Entomopathogens are particularly well suited to this. A furtherembodiment is to use as the pesticide a specific attractant to attractinsects to the composition. For example, the attractant may be a sexualpheromone. Furthermore, a sexual attractant pheromone may be used toproduce male confusion. This technique depends on the very highsensitivity of male insects to volatile sex attractants produced byfemales of the same species. (In a few cases the male produces theattractant). The female pheromone affects the male guidance system whichdepends on flying upwind in an odour laden air current, therebydisrupting mating by preventing the males from locating the females.

Alternatively, a surface on which the insects may land is coated withelectrostatically charged particles containing a volatile pheromone. Theparticles are then picked up by the insect from the surface. Theparticles picked up in this way are then transferred to the antennae orother parts of the insect bodies either by exploratory movement orduring cleaning. The particles remain in place and continue to releasepheromone, the coating on the particle ensuring good attachment andcontrolling the release rate. Due to habituation or saturation of theantenna receptors by the pheromone emission, the insects are unable toorientate with respect to trace emissions of pheromone from femaleinsects in the air. Mating fails to occur and eggs laid by the femalesare infertile. Furthermore, the males themselves act as female mimics,diverting uncontaminated males away from calling females.

In a particular embodiment of the invention the electrically resistivecoating is smooth. The smoothness of the coating will depend upon thenature of the coating material and the coating technique used.Accordingly, insects or mites which contact the smooth coating oncharged particles get the particles onto their feet and the smoothsurface of the particles reduces friction and prevents them grippingsatisfactorily onto a surface on which they are crawling. For example,honey bee mites (Varroa) are prevented in this manner from crawling upthe walls of the beehive and attaching to bees. They thus fall to thebottom of the hive and then are killed by an acaricide contained withinthe particles, by techniques known in the art.

In a preferred aspect of the present invention, a second pesticide orherbicide may be adhered to the coating of the electrically resistivematerial, i.e. on the outer surface of the composite particles.

Particles which have two pesticides associated therewith may have twopossible modes of action on the same species of insect. For example, thepesticide impregnated into or associated with the inert substrate may bea bacillus which is toxic to the insect on ingestion. The secondpesticide may be a fungus which is toxic by invasion through the outercuticle of the insect.

The number of pesticides incorporated into a single particle may beregulated in order to achieve a desired range of target specificity, orparticles having different constituents may be mixed to achieve the sameend.

Alternatively, the composite particles of the present invention maycontain a herbicide. For example, the herbicide may be a weedkillerwhich is sprayed onto a crop and will attach both to the crop plants andany weeds growing with the crop. The weedkiller then kills the weeds.Alternatively, the crop plants may be sprayed or dusted with herbicidecontaining particles to achieve another effect, such as promoting ordelaying growth.

In situations where particular insect pests or fungal pests attack acrop, a suitable pesticide for the insect or fungi may be incorporatedinto the particles and the crop plants sprayed or dusted with thecomposition. The insects or fungal spores thus come into contact withthe particles which adhere to them and the pesticide is released fromthe particles of the composition to kill the insects or fungal spores.Combined compositions comprising herbicides with insecticides and/orfungicides are contemplated within the scope of the invention.

Charging of the particles may be achieved by friction or by subjectingthem to electrical discharge, high electrical fields or other suitablemeans. Where the particles are applied directly to the pest, plant orsurface for instance, by a dispenser, such as, an aerosol spraydispenser, frictional charging may be effected by suitable design of thedispenser, particularly the nozzle configuration thereof.

The particles of the present invention will preferably retain theirelectrostatic charge for at least 24 hours when they contain slow actingchemical pesticides, such as chemical insecticides and for at least 4 to5 days when they contain biological pesticides.

The present invention will be further described with reference to theaccompanying drawings, in which:

FIG. 1 illustrates a particle of a control agent in accordance with theinvention.

Referring to FIG. 1, the particle 4 comprises a highly absorbent orporous core 1 surrounded by an electrically resistive coating 2. Thecore 1 is impregnated with a pesticide, for example a biologicalinsecticide such as Metarhizium anisopliae. The electrically resistivelipid coating may be, for example, carnauba Wax.

As illustrated in FIG. 1, the particle 4 has a further pesticide 3applied to the outer surface of the coating 2. The further pesticide maycomprise fungal spores. A plurality of particles as shown in FIG. 1 maybe charged by corona discharge techniques.

The present invention will be further described with reference to thefollowing Examples.

EXAMPLE 1

Silicon dioxide particles 0.5 to 10 μm in diameter, (Sigma ChemicalCo.), 10 g, were mixed with log of the insecticide Sulfluramid (TradeName—Griffin Corporation). Composite impregnated silicon dioxideparticles were thus formed which were then throughly mixed with 80 gCarnauba wax particles of from 20 to 80 μm in diameter. The silicaparticles, which are known to occlude lipid materials acquired a coatingof lipid molecules from the wax particles. Carnauba wax is a highlyelectrically resistive material. Accordingly, the addition of the wax tothe silica particles, and coating of the silica particles thereby,increases the level of charge imparted to the particles as a result offriction on shaking the powder.

10 adult German cockroaches (Blattella germanica) were treated with theprepared dry powder mixture using a fine camel hair brush to place afine uniform coating over the whole of the dorsal surface of the insect.For each group of 10 insects that was treated with the mixture, asimilar group was treated in exactly the same way with a mixtureprepared in the proportions of silica, 90 g, and sulfluramid, 10 g. Eachtest was replicated four times with each group of 10 insects.

The treated cockroaches were kept in individual containers in a chamberat 25° C. and 30-40% relative humidity. The mortality of the insects wasthen recorded in terms of the number of insects out of 10 that showed nomovement of any part of the body for 24 hours.

FIG. 2 shows the mean mortality of cockroaches from the four replicatetests. The results show that the insecticidal effect is significantlygreater when the electrostatic properties of the carrier particles areincreased by association with the wax particles. This is demonstrated bymortality occurring after 72 hours with the wax coated silica particles,rather than after than 96 hours for particles without the wax coating.

EXAMPLE 2

The procedure of Example 1 was repeated using chitosan (Seacure CL210,Pronova Biopolymer) as the carrier for the sulfluramid.

A control experiment was carried out substantially in the manner asdescribed in Example 1 using a mixture of chitosan and sulfluramid.

The results of the experiments are given in FIG. 3, from which it can beseen that the insecticidal effect of the sulfluramid is increased whenthe carrier particles are coated with lipid.

EXAMPLE 3

The procedures of Examples 1 and 2 were repeated using adult Americancockroaches (Periplaneta americana). Substantially the same results wereobtained.

What is claimed is:
 1. A pesticidal composition in particulate formwhich comprises composite particles having an average particle size inthe range of from 1 to 100 μm, each particle comprising a core of aninert substrate having a first pesticide associated therewith, a coatingof an electrically resistive material around said core, and a secondpesticide adhered to the coating of electrically resistive material, theparticles carrying an electrostatic charge.
 2. A composition accordingto claim 1 wherein the particles have an average particle size in therange of from 20 to 60 μm.
 3. A composition according to claim 1 whereinthe inert substrate comprises silica, magnesium silicate, diatomaceousearth, cellulose or a natural or synthetic polymer.
 4. A compositionaccording to claim 1 wherein the first pesticide is an insecticide,fungicide, acaricide, insect growth regulator or chemosterilant.
 5. Acomposition according to claim 1 wherein the first pesticide is abacterium, virus or fungus.
 6. A composition according to claim 1wherein the first pesticide is a behaviour modifying chemical.
 7. Acomposition according to claim 1 wherein the first pesticide comprisesat least 0.1% by weight of the core of the particles.
 8. A compositionas claimed in claim 1 wherein the electrically resistance coatingmaterial comprises from 5 to 25% by volume of the particles.
 9. Acomposition as claimed in claim 8 wherein the coating comprises a wax, alipid, a natural or synthetic resin or a natural or synthetic polymer.10. A composition as claimed in claim 1 wherein the second pesticidecomprises fungal spores.